The present invention relates to a direct-injection, spark-ignition engine having a turbo-charging device.
Recent environmental requirements have necessitated improvements in fuel efficiency of automotive spark-ignition engines to improve energy savings and reduce CO2 (carbon-dioxide) emissions. Under these requirements, a direct-injection, spark-ignition engine has been recently developed wherein fuel is directly injected into the combustion chamber to collect for stratification in the vicinity of the spark plug, for enhancing ignitionability, while causing the air-fuel ratio to have a lean stoichiometric air-fuel ratio for improving fuel efficiency.
An engine having a turbo-charging device which attains the increase in engine output by means of high intake-pressure, or high charging-efficiency caused by the efficient use of the high exhaust-gas pressure in the automotive engine, is also known. Such an engine has been noted in recent years for its effectiveness in providing a leaner air-fuel ratio.
Normally, a catalyst converter adopting an exhaust-gas purification catalyst is disposed in an exhaust-gas passage of an engine. The catalyst purifies pollutants such as NOx (nitrogen-oxides), HC (hydrocarbon), and CO (carbon-monoxide) included in the exhaust gas emitted from the combustion chamber of the engine of the automobile. The exhaust-gas purification catalyst generally has sufficient purification for an exhaust-gas having a temperature higher than its activation temperature and insufficient purification for the exhaust-gas having a lower temperature than the activation temperature.
Accordingly, when the engine starts in a cold state, the exhaust-gas purification catalyst is not activated for a certain time period after the engine starts. To reduce pollutants immediately after a cold start, the exhaust-gas purification catalyst is required to rise in temperature rapidly to attain early activation.
In an engine having a turbo-charging device, however, a turbine of the turbo-charging device is disposed in the exhaust-gas passage, and the catalyst converter is disposed downstream of the turbine. With this arrangement, there is a problem that the temperature rise, or the activation of the exhaust-gas purification catalyst, is delayed in cold-start because the turbine cools the exhaust gas to, for example, 100xc2x0 C. To avoid this problem, the catalyst converter may be arranged upstream of the turbo-charging device. In this case, however, the catalyst converter is located immediately downstream of the combustion chamber, so that the exhaust-gas purification catalyst is unduly heated when the engine is fully heated, causing the problem of degradation in its durability due to the heat. In addition, the flow resistance due to the catalyst converter being located upstream of the turbine inevitably causes turbo lag, which impairs acceleration response in the turbo-charging device.
In view of the above problems, numerous solutions have been proposed. One such approach is a supercharged engine which lowers its turbine rotational speed during cold start to suppress heat transmission from the exhaust gas to the turbine for promoting temperature rise or activation of the exhaust-gas purification catalyst. See, Japanese Patent Publication No. H9-100724.
Another approach is disclosed in Japanese Patent Publication No. H10-212987, wherein in a direct-injection, spark-ignition engine the fuel being injected is divided in two, or the fuel is injected during the intake stroke and the compression stroke in cold start, to increase the temperature of the exhaust gas for promoting temperature rise or activation of the exhaust-gas purification catalyst.
Another direct-injection spark-ignition engine has been also proposed, in which fuel is injected during the intake stroke and in the compression stroke during a predetermined period after cold start, then fuel is injected in the compression stroke and in the expansion stroke after that period, to increase the temperature of the exhaust gas for promoting temperature rise or activation of the exhaust-gas purification catalyst. See, Japanese Patent Publication No. 2000-120471.
Recently, emission standards for automotive engines have become more strict, requiring the engines to activate their exhaust-gas purification catalysts within approximately 30 seconds after cold start. However, the conventional approaches to promoting activation of the exhaust-gas purification catalyst in cold start, as disclosed in Japanese Patent Publication Nos. H9-100724, H10-212987, and 2000-120471 described above, may be insufficient for promoting the temperature rise or activation of the exhaust-gas purification catalyst under these newer, stricter emission standards. Accordingly, the auto industry seeks more effective approaches for promoting activation of the exhaust-gas purification catalyst.
In view of the above, an object of the present invention is to provide an approach to sufficiently promote the temperature rise or activation of the exhaust-gas purification catalyst which is disposed downstream of the turbine in the exhaust-gas passage, in a direct-injection, spark-ignition engine having a turbo-charging device, during cold start.
In accomplishing this and other objectives of the present invention, there is provided a direct-injection, spark-ignition engine having a turbo-charging device. A piston compresses the injected fuel. A fuel injector directly injects fuel into a combustion chamber. An ignition device ignites the injected fuel. An exhaust-gas purification catalyst is disposed downstream of a turbine of the turbo charging device in an exhaust-gas passage. A fuel injection controller controls the amount and the timing of the fuel injection by the fuel injector. An ignition controller controls the ignition timing by the ignition device. An intake-air controller controls the amount of intake-air introduced in the combustion chamber. The fuel injection controller causes the fuel injector to divide fuel injection into a leading fuel injection during a leading period of an intake stroke of the piston prior to the ignition timing, and a trailing fuel injection during a trailing period of an expansion stroke after the ignition timing for a predetermined operating condition, where the exhaust-gas purification catalyst is to be activated. A fuel injection controller controls the fuel injector and the intake-air controller controls the amount of intake-air so that the excess air ratio xcex in the combustion chamber is larger than 1, when the combustion of the fuel by the trailing fuel injection and the leading fuel injection completes.
Preferably, at low engine rotational speed and low engine load, the fuel injection controller controls the fuel injector and the intake-air controller controls the amount of intake-air, so that the excess air ratio xcex in the combustion chamber is within the range of about 2 to 3 when the fuel of the leading fuel injection combusts.
Accordingly, the fuel injected by the leading fuel injection combusts under high volumetric efficiency (xcex7v) with a leaner air-fuel ratio of xcex of 2 to 3 (this condition is referred to as xe2x80x9ca leading combustionxe2x80x9d). Additionally, fuel of the trailing fuel injection effectively combusts because of a leaner air-fuel ratio (exhaust-gas air-fuel ratio) of xcex smaller than 1 at the combustion (this combustion is referred to as xe2x80x9ca trailing combustionxe2x80x9d). At this time, the trailing combustion raises the exhaust-gas temperature. Moreover, the turbine of the turbo-charging device agitates the exhaust-gas (this agitation is referred to as xe2x80x9cturbine agitationxe2x80x9d). The turbine agitation causes unburned HC in the exhaust-gas to oxidize (afterburn), and this exotherm further raises the exhaust-gas temperature. In this manner, exhaust-gas temperature is raised from heat generated by the trailing combustion and by the oxidization of the unburned HC from the turbine agitation to greatly raise the exhaust-gas temperature, for effectively promoting the temperature rise or activation of the exhaust-gas purification catalyst downstream of the turbine.
Preferably, the predetermined operating condition may be where the exhaust-gas purification catalyst is in an inactivated state. In the early stage of the inactivated state, the ignition controller may cause the ignition device to ignite at a timing after MBT by a predetermined period and the fuel injection controller may cause the fuel injector to inject fuel prior to the ignition timing. In the late stage of the inactivated state, the fuel injection controller may cause the fuel injector to divide fuel injection into a leading fuel injection during a leading period of the intake stroke prior to the ignition timing, and a trailing fuel injection during a trailing period of the expansion stroke, after the ignition timing the fuel injection controller controls the fuel injector and the intake-air controller controls the amount of intake-air, so that an exhaust-gas air-fuel ratio after the combustion of the fuel by trailing fuel injection is lean of the stoichiometric air-fuel ratio.
Accordingly, in the early stage of a condition where the exhaust-gas purification catalyst is in an inactivated state, or when engine temperature is relatively low, because the ignition timing is retarded to the timing after MBT, the exhaust-gas temperature rises to promote warm-up of the engine and temperature rise in the exhaust-gas purification catalyst. Under this condition, the temperature rise in exhaust-gas by the fuel injection in the expansion stroke, after the ignition timing (without ignition retard), is less than that by ignition retard. This is because relatively low temperature in the engine or the exhaust-gas in this condition causes poor combustionability of the fuel injected during the expansion stroke, and the agitation of the exhaust-gas by the turbine (referred to as turbine agitation) described later causes little oxidization of the unburned HC (afterburn).
On the other hand, in the late stage of a condition where the exhaust-gas purification catalyst is in an inactivated state, relatively high engine temperature or the exhaust gas and lean air-fuel ratio (with the sufficient amount of oxygen), maintain combustionability of the fuel by the trailing fuel injection (avoiding misfire), so that such a combustion raises the temperature of the exhaust-gas and the turbine agitation promotes oxidization of the unburned HC to further raises the exhaust-gas temperature. Under this condition, the temperature rise in exhaust-gas by ignition retard (without fuel injection in the expansion stroke) is less than that by the trailing fuel injection. In this manner, in cold start, the most effective approach to promoting the temperature rise in the exhaust-gas is selected, so that the exhaust-gas purification catalyst can be heated or activated early.